The present invention relates to a compact and lightweight zoom lens mount barrel.
There has been heretofore provided a zoom lens mount barrel having a separate cam or drive sleeve including a plurality of cam or lead slots therein for moving front and rear lenses in the optical axis direction. For this reason, it is very difficult to miniaturize the zoom lens mount barrel diameter. Also, disadvantageously, in the prior art mount barrel a suitable washer must be inserted between the lens mount and the fixing member thereof in order to adjust the distance from the end of the lens to the image surface. Because of this, the prior art adjustment mechanism required a complex assembly operation.
Referring to FIG. 1 showing a prior art zoom lens mount barrel, reference numeral 1 designates a lens mount, 2 a rear distance minute adjustment washer, 3 a fixed sleeve attached to the lens mount 1, 4 a zoom operational ring or sleeve, 4a an axial groove formed along the optical axis in the zoom operational sleeve 4, and 5 a drive sleeve slidably disposed within a forwardly extending portion 3a of the fixed sleeve 3 and in which is provided cam slots 5b and 5c and a pin 5a which is engaged with the above described axial groove 4a. An escape slot 3b is circumferentially formed in the fixed sleeve 3. A first support frame or sleeve 6 supporting a front lens group 1 is provided with a pin 6b which engages with the above-described cam slot 5c. A second support frame or sleeve 7 supporting a rear lens group II is provided with a pin 7a which engages with the above described cam slot 5b, a guide slot 6a formed parallel to the optical axis in the support frame 6 and a guide slot 3d formed parallel to the optical axis in a forwardly extending portion 3c of the fixed sleeve 3. The above described support frames 6 and 7 are engaged respectively with the exterior and interior surfaces of the extended portion 3c of the fixed sleeve 3. The front lens group I is independently moved back and forth by the rotation of the distance operational barrel or sleeve 8 to thereby achieve focusing. An index barrel 9 is coupled to the fixed sleeve extended portion 3a.
With this construction, when the zooming operational sleeve 4 is rotated, the drive sleeve 5 and hence the cam slots 5b and 5c are rotated together due to the engagement of the pin 5a and the groove 4a. On the other hand, the pin 7a and hence the second support frame 7 are prevented from rotating by the slot 3d while the support frame 6 and hence the pin 6b are also prevented from rotating. As a result, the support frames 6 and 7 are moved in the axial direction to achieve the zooming.
As may be seen from FIG. 1, the zooming mechanism includes six layers, namely, in order from the outside, the zooming operational sleeve 4, the fixed sleeve extended portion 3a, the drive sleeve 5, the front lens group support frame 6, the fixed sleeve extended portion 3c and the rear lens group support frame 7. Therefore, because of the relatively high number of layers, the outer diameter of the lens mount barrel must necessarily extend quite far beyond the periphery of the lens groups. Also, since the final dimensional adjustment for the rear distance from the rear end of the lens to the image surface is only known after the thickness of the washer 2 has been determined and the zoom lens assembled, the assembly operation of the zoom lens is time-consuming and troublesome.